Multiple sites, same blog

I’ve installed wordpress in three different directories on my site and got all three of them configured to display exactly as I want them. But, I don’t want to have to go to the effort of re-posting three times every time I’m adding a blog post, so I’m looking for a way to tell two of my wordpress directories to access the blog information from the third directory. I’ve tried several different plugins that will re-post things for me, but the best I’ve managed to do only shows an excerpt on the front page of the other two sites instead of posting the whole thing, no matter what configuration tricks I try to toy with. I’m thinking getting them all to access the same blog information will by ideal, anyway, since it’ll synchronize comment threads, as well, but I’ll be happy if the closest I can get is replication. I’m not much of a web developer myself, so I’m sure this is a pretty easy problem to solve for the likes of the WordPress community. Anybody got any pointers?